Figure 1. At the NEES Large-Scale Lifelines Testing Facility at Cornell University, Michalowski’s team applied sensors to the concrete pipeline before burying it in the test tank. The cutaway shows the wireless transmitters buried with the pipe. (Image: Radoslaw Michalowski, University of Michigan)

After an earthquake, infrastructure damage can be difficult to detect. In particular, cracks and breaks in underground water pipelines often can’t be identified without excavating the pipes and physically inspecting them.

Obviously, securing lifelines is a high priority for post-quake repairs; undetected or inaccurate information about damage to water-delivery networks can lead to epidemic outbreaks in communities hit by natural disasters.

But imagine if underground pipes alerted repair workers to problems. What if damaged pipes were able to send wireless messages that signaled where and how they were damaged?

Cutting-edge earthquake engineers are seeking to design “smart,” self-sensing concrete pipes that allow for this very scenario.

Towards “smart” pipes

For the first time, earthquake engineers conducted large-scale tests on buried segmental concrete pipelines to understand exactly how water pipes fail during earthquakes.

Thanks to a four-year study led by principal investigator Radoslaw Michalowski, professor of civil engineering at the University of Michigan, these damage-assessment tests mark the first-steps toward the development of strategies for wirelessly detecting damage and monitoring the structural health of pipelines.

Michalowski explained, “Simply put, the application of sensors and wireless technologies will change the way we maintain our infrastructure.”

Michalowski and his multidisciplinary research team, including Jerry Lynch of the University of Michigan, a specialist in sensors and sensor networks, Jason Weiss of Purdue University, a specialist in concrete pipelines, Russell Green of Virginia Tech, an earthquake specialist, and Aaron Bradshaw of the University of Rhode Island, a specialist in off-shore engineering, envision that future lifelines will be “smart structures,” pipes built of materials with self-sensing capabilities. Ultimately, wireless techniques will be used to transmit the information-carrying signals from several feet underground to the surface, where problems can be identified without excavation.

Dr. Michalowski’s research was sponsored by the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES). NEES is an NSF-funded network of 14 sites that share equipment and simulation tools as well as a robust cyberinfrastructure.

The experiments on buried pipelines were carried out in the NEES Large-Scale Lifelines Testing Facility at Cornell University, where a large test tank -- with holding capacity of over 100 tons of sand -- enables engineers to test full-scale soil-structure interactions during ground rupture.

Figure 1 shows the team preparing the pipe in the test tank.

Large plates line the base of the test tank. During testing, the plates shift laterally with respect to one another, causing ground displacement, which simulates the ground rupture that occurs during earthquakes.

The team buried sensor-laden pipes, subjected them to simulated ground rupture, and collected data in order to discover the best methods for employing wireless transmitters for signaling from underground sensors.

Testing buried pipelines

The commercial-size pipe consisted of five, eight-foot concrete segments. Before burying the pipe in 100 tons of sand, the team applied an extensive array of sensors to monitor pipe behavior when subjected to ground movement. The sensor system included strain gauges, potentiometers (to measure displacements), conductive concrete grout (self-sensing material), magnetic sensors, self-sensing fiber-reinforced concrete, an acoustic emission monitoring system, electrical tape sensors, and fiber optics. Much of the data transmission during the test occurred wirelessly from buried transmitters, which were designed and manufactured at the University of Michigan.

Determining failure modes

The sensors revealed the sequence of the failure for buried segmental concrete pipelines. Researchers noted that failure starts with the grout in the pipeline joints; this was detected thanks to self-sensing cement-based grout material and the acoustic emission detection system.

When subjected to increasing ground displacements, the pipe damage first concentrated in the bell-and-spigot joints closest to the ground fault, and to a lesser extent in the joints further away from the fault. Joint rotation and “telescopic” movement were identified as two major modes of pipeline failure. Examples of a severe damage to pipeline joints caused by ground rupture are illustrated in Fig. 2.

Self-Sensing: the future

Using data collected from the experiments, Michalowski and his team are now developing protocols for rapid, wireless damage assessment, obviating the need for pipe excavation.

Michalowski is pleased with the project’s results. “Over the course of 4 years, in addition to faculty members from five universities and highly skilled technicians, we had twenty six students involved in the project. I couldn’t ask for a better team.”

As the first effort toward the design of self-sensing systems for buried pipelines, this project will have significant impact on the maintenance of all buried lifelines.

Michalowski revealed, “The next step in our research will be to develop methods for detecting damage, particularly corrosion damage, in the types of metal pipes that carry natural gas and petroleum products.”

Smart, self-sensing structures provide the most efficient way for repair crews to gather, process, and act on data about the structural integrity of buried pipelines.

Clearly, this earthquake engineering research will have broad applications in managing multiple types of physical infrastructure, including tunnels, telecommunications, and other types of buried lifelines.